Ser Jaime Lannister, perhaps the most notable example of a kingslayer, who killed Aerys II Targaryen during the Sack of King's Landing. Jaime's actions were considered especially heinous, as he was in fact a member of Aerys' own Kingsguard, and took a holy vow to lay down his life in defence of his king[1] Jaime killed Aerys in order to foil his scheme to destroy King's Landing, but since he never revealed it to anyone (except recently to Brienne) - everyone assumed he killed Aerys so the Lannisters would seize the throne. It is unknown whether Jaime would still bear the stigma of kingslayer if he revealed his real motive.

Khal Drogo murdered Viserys Targaryen by pouring molten gold onto his head. Despite technically being the rightful king of Westeros, Viserys himself was an exile at the time, and never actually sat upon the Iron Throne.[2]

Queen Cersei Lannister, along with her cousin Lancel, conspired to bring about the death of her husband King Robert Baratheon. On Cersei's instruction Lancel replaced the wine in the king's flask with a stronger, fortified vintage, causing Robert to quickly descend into an intoxicated state, dulling his reflexes, and ultimately leading him to suffer a fatal wound upon a boar's tusk.[3]

King Stannis Baratheon, who conceives a shadow assassin with Melisandre to kill his brother Renly. This may not be considered a true example of kingslaying, as Renly himself was a usurper, and was in open rebellion against his elder brother, the rightful king. Moreover, Renly never officially sat upon the Iron Throne.[4]